The present invention relates to a process for producing maleic acid with minimal production of fumaric acid.
Production of maleic acid (MA) is known in the art as being the reaction product of hydrolysis of maleic anhydride (MAH). A typical example is described in Kirk-Othmer, Encyclopedia of Chemical technology, third edition, Vol 14, page 778, wherein the process for producing MA is carried out at room temperature. The MAH is usually added in solid state. However, a problem encountered at room temperature with solid MAH is the resulting slow reaction rate. Still another problem encountered with the use of solid MAH is that it is difficult to handle when used in industrial quantities. Indeed, solid MAH is more difficult to pump, store and meter in an accurate manner compared to liquid MAH.
A solution to this problem is the production of MA in a batch, i.e. adding MAH to hot water. However, whilst this solution provides effective reaction rate, due to the exothermic reaction and resulting temperature rise, fumaric acid will also be produced in undesirable quantities as a by-product, that is higher than 0.4% by weight of the resulting reaction mixture.
Indeed, as the reaction between MAH and water is exothermic, the temperature within the reactor and thus the temperature of the reaction mixture increases. This rise in temperature favours the formation of fumaric acid instead of MA. Fumaric acid, to a certain extent, is an undesirable by-product product as it tends to precipitate at low concentrations, e.g. 0.4% by weight at room temperature. Furthermore, when incorporated in cleaning compositions, it has been found that fumaric acid compared to compositions containing MA has a lower performance towards limescale removal.
Accordingly, it is an object of the invention to provide a process with optimum conversion of MAH into MA and minimal production of fumaric acid.
It has now been surprisingly found that the use of a substantially constant temperature throughout the whole production process, that is from the contacting step of the reactants to the recovering step of the MA, fulfills such a need.
The present invention is a process for the production of maleic acid from maleic anhydride and water which comprises the steps of:
a)-contacting maleic anhydride and water to form a reaction mixture;
b)-recovering maleic acid from said reaction mixture; and
characterised in that said reaction mixture is maintained at a substantially constant temperature within the range of 52xc2x0 C. to 85xc2x0 C. during step a) and b).